Research was completed on the collection of thermodynamic data on the oxygen up-take by synthetic oxygen carriers of various cobalt(II) Schiff base and macrocyclic complexes. The oxygen up-take ability of these cobalt chelates was found to quantitatively correlate their oxidation potentials (Co(II) yields Co(III) plus e). Experiments with simple iron porphyrins such as Fe(TPP)(B)2, where TPP equals meso-tetraphenylporphyrin and B equals 1-methylimidazole, pyridine or piperidine, show that at low temperature solutions of these systems are good oxygen carriers. The oxygen adds in the form of the monoadduct Fe-O2, and these species are being investigated spectroscopically in an attempt to learn something about the nature of the Fe-O2 bonding. Kinetic studies are also in progress on the addition and release of O2 from these systems. It has been possible to prepare the system silica gel-imidazole-Fe (TPP) which has the iron porphyrin attached to the modified silica gel through imidazole. One coordination site on the iron is vacant, and this site readily and reversibly adds oxygen. Detailed studies are in progress on various heterogeneous systems of this type.